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IC overheating.

I'm working on a little fanspeed regulator circuit. This specified debouncing circuit wasn't working at all (bad switch?), so I substituted a design known to work that used a not-gate (LS04). It warks fine, but the problem is that the LS04 chip heats up pretty quickly, then eventually gets too hot to leave it plugged in. I searched the layout, and checked all the connections, but couldn't find any shorts or bad connections. I had a different chip before (I think a display driver) that was set up propperly on a breadboard but burned up too, leading be to believe that it was just a bad chip. So its possible that the chip I have (04) is just bad, and may have been damaged during soldering. Does this theory fly with any body else?

Is there anyhing I can do to fix it without using another chip? Ground outputs, etc? Has anybody had a 'bad' chip that burns up right out of the box? Does the idea of soldering sound like a cause of overheating?

Cheers.

Reply to
ghosttwo
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Assuming power is applied to the right pins, the only load situation that normally heats up TTL is to have an output tied to the positive rail. Of course, inputs or outputs connected to voltages outside the rails may cause the chip to turn into and SCR that shorts the supply rails.

Reply to
John Popelish

Sounds like they overfilled the chips with magic smoke, has any escaped yet ?

dont ground outputs, but ground any unused inputs, make sure outputs arnt overloaded, and supply voltage or any other inputs havnt got any over voltage peaks etc.

Colin =^.^=

Reply to
colin

I've had chips get too hot to touch by plugging them in backwards. =:-O

Good Luck! Rich

Reply to
Rich Grise

More likely the unused gates are oscillating, or you're pulling too much current from the gate that you are using. Try tying all your unused inputs together & connecting them to +5V with a 4K7 resistor. Also check that Vcc (pin 14) is really at +5V relative to the ground pin (pin 7).

Reply to
Lionel

I've had them work afterwards. (it was a 7555)

--

Bye.
   Jasen
Reply to
jasen

This thing is getting on my nerves. I got some wire and stuff, and made a breadboard to molex adapter, and it worked flawlessly. No overheating, no problemo. I try it in the Pc however, and it burns up like fire. It doesn't matter if the fan is plugged into it or not So I start looking at the differences between the working (breadboard) and nonworking (PC) states. First I notice that with my little adapter, the two grounding rails (black wires) are tied together, but not in the PC. So I bridge them together. Breadboard mode still works, but Pc doesn't. So then I think, "with the B.B, theres only one ground, while the PC has two. So I remove a pin from the molex, same deal. So I give up for a while and watch some sopranos. A little later I try it in the pc again. It works. It normally gets hot in less than a minute, but this time it didn't. I leave it plugged in and keep checking it. Five minutes go by, then ten. A few hours later, its a little warm, but not hot. Its been plugged in for over eight hours and its still cool. I don't know why.

Before I tried it again, I messed with the wires in the PC, testing the voltages in the cables. I don't have time to go into detail, but it seems as if one of the fans were plugged in upside-down, effectively swapping the +5 and +12 rails. Not good. I'm going to monitor it for a few days, and maybe add a feature or two. But this may be the big 'Problem Solved', and I sure hope it is.

Reply to
ghosttwo

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